1. Field of the Invention
This invention relates to computer peripheral data communications equipment. In particular, it relates to computer terminals and/or man-machine interfaces, used by individuals to communicate text and graphic information.
2. Description of Prior Art
Prior art in the field generally involves computer terminal units where conventional display devices are electrically connected to a graphic tablet or touch panel device. A display device is defined as an electrical and/or optical device capable of visually presenting alphanumeric, line graphic, or pictorial information onto a viewing screen. A display panel is a component of some display devices, which consists of an electrooptic material sandwiched or placed between two substrates, on which the visual information is written by electrical or optical means. An electrooptic material is a homogeneous material which changes optical state when an electrical field and/or light beam is applied. Generally, display devices can be classified as either a direct view or indirect view display. Henceforth, in this specification, a direct view display will mean that the display panel of the device is also the display screen, and the screen is large enough to be viewed by a person. An indirect view display is a display device where the display panel is separate from the screen, and the visual information is first placed onto a small display panel and then optically projected onto a larger screen.
Most display device prior art involve the well known cathode ray tube (CRT) or the flat panel display technologies. Examples of the flat panel display technologies include the electrooptic panels, plasma panels and electroluminescent displays. The flat panel displays are addressed, i.e., a point or small area of the panel is selected to be written or erased, by either a conductor matrix means or a light beam means. An electrooptic material is capable of changing optical state from electrical stimulus. Most common electrooptical materials are liquid crystal (LC), electrophoretic and electrochromic materials. These displays are usually matrix addressed. Examples of light beam addressed displays include laser and light emitting diode sources which optically address various flat panels cells or display screens.
The most prevalent high information content display is the conventional CRT display, as used in standard television. Nevertheless, the CRT display has several disadvantages well known to those in the field These disadvantages are important especially when used in desk top computer terminal applications. Disadvantages of the CRT display include: (1) the CRT usually has a long neck resulting in a bulky display device; (2) the CRT requires large operating voltages; (3) the CRT resolution is limited to focusing of its electron beam; (4) the CRT display screen is not flat but curved, usually in a spherical shape; (5) the CRT emits an electromagnetic radiation; and (6) the display does not have inherent memory and must be constantly refreshed.
The most common electrooptic materials used in displays are LC materials, and most of these LC Displays (LCD) are the matrix addressed type. Matrix addressed display panels are those that have a matrix of orthogonally cross conductors serving as the electrodes, forming an array of display cells. Prior art in matrix addressed LCD panels include the disclosures: U.S. Pat. No. 3,994,567 of Matsuo, Toida and Tsunoda, 1976; A. R. Kmetz, S.I.D. Digest, 1972; and B. Lechner, F. Marlow, E. Nester and J. Tults, Proceeding of the IEEE, Vol. 59 No. 11, November 1971. However, matrix addressed electrooptic displays suffer from several disadvantages, especially for large display sizes. First, they are difficult to fabricate because of the large number of wires that must be connected to the panel. For a matrix display equivalent to a television picture, approximately 600 connections must be made to the panel. Secondly, complex multiplexing electronics must drive each panel row and column conductor, adding to the cost. Thirdly, the lack of a sharp optical threshold in electrooptic materials limits the number of picture elements that can be written and the rate at which they can be refreshed. Finally, matrix displays have practical limits in the number of picture elements per panel and in display resolution due to fabrication techniques. The highest resolution matrix display possible with conventional manufacture techniques is about 400.times.400 picture elements, which is too low for most display applications.
For high resolution display applications having a large number of picture elements, an optical beam addressed electrooptic display device is desired. This is the type of display that is of primary interest in this specification. Prior art in optical beam addressed electrooptic displays include U.S. Pat. No. 4,422,732 of Ditzik granted Dec. 27, 1983, which disclosed a beam addressed electrooptic display system that is scanned by a moving optical fiber element, where the optical beam is cross-sectionally shaped. This prior art display system has some limitations which have been substantially improved by the inventions specified herein. Improvements over this prior art consist of: (1) the addition of a graphic tablet device for man-machine interaction; (2) the use of a flat field projection lens for improved beam focusing; (3) the elimination of several electrooptical components; and (4) a simplified folded optics design.
Other prior art in beam addressed electrooptic displays include U.S. Pat. No. 3,775,757 of Taylor and Ferguson, U.S. Pat. No. 3,720,784 of Maydon and Cohen and U.S. Pat. No. 3,796,999 of Kahn. Each of these used an LCD panel onto which data is written by a low power laser beam. However, this prior art suffers from several disadvantages which has prevented them from being manufactured and marketed successfully. These display systems are indirect view systems requiring independent writing and readout optics. Such display systems require a high intensity lamp, expensive projection optics, and a separate viewing screen. In each of these prior art systems the display panel is small (1-2 inches square); so direct viewing of the panel is not possible. Another disadvantage of an indirect view display is that room ambient lighting must be reduced in order to obtain acceptable screen contrast.
Prior art in graphic tablets have been limited to separate opaque tablets used for scientific or computer-aided design applications. The limitations of these opaque tablets are obvious; they cannot provide an interactive electronic writing surface, because the user must continually look up from the tablet writing surface to the display screen. A graphic tablet can be defined as a device comprised of an electronic writing surface on which a person can position a hand-held stylus, and the position where the stylus touches is measured in two dimensions (x and y). The measured position is converted into an electrical digital code (i.e., encoded) in a conventional manner. The stylus may be a pen or any narrow object or instrument. As one moves the stylus, tracing a path over the writing surface, a continuous digital data stream is output to a display device or other devices. The stylus tracings can be viewed on the display device as graphic information. The design and operation of the graphic tablet input device is known to those practiced in the art; e.g., reference U.S. Pat. No. 3,524,998 of Gilbert; United Kingdom Patent 1,133,757 of Ellis; and M. R. Davis and T. O. Ellis (Proceedings--Fall Joint Computer Conference, 1964).
There is little prior art in the use of display devices in combination with a graphic tablet. A graphic tablet integrated with a display device and operated in combination is henceforth referred to as a display-tablet system. Davis, Garrett, Kirkman and Wiseman disclosed an interactive display tablet that uses a miniature electrochromic or LCD panel which is projected onto the rear of an inclined screen surface (IBM Technical Disclosure Bulletin, Vol. 25, No. 118, April 1983). However, the disadvantages of this disclosure are: (1) the display requires a high intensity lamp and optics for information read-out of the miniature panel, (2) two mirrors are required to fold the optics; (3) the screen is limited to small sizes due to the geometry of the optics required.